1. Field of the Invention
This invention relates to single-polarization fiber optics magnetic sensors.
2. Description of the Prior Art
A typical prior art single-polarization fiber optics magnetic sensor is described with reference to FIG. 1. A light source 1 emits light which is focused through a focusing lens 2 into one end of an optical fiber 3 which transmits the light to the other end. The light exiting from the optical fiber is converted into parallel rays through a collimator 4, which are passed through a polarizer 5 which produces linearly polarized light. This linearly polarized light enters a Faraday rotation element 6 and is derived out as signal light through an analyzer 7 optically coupled to the exit of the element 6. The signal light is received by a photo-detector 8 which is electrically connected to an instrument 10 through a lead 9. The orientation of the polarizer 5 and the analyzer 7 is set to 45.degree. or 90.degree..
In this arrangement, the positioning of the polarizer 5 and the analyzer 7 at the opposite ends of the Faraday rotation element 6 is indispensable. In the case of usual single- or multi-mode fibers, if the polarizer 5 is inserted between the light source 1 and the optical fiber 3, then the incident light to the Faraday rotation element 6 will generally become elliptically polarized light rather than linearly polarized light. It is obvious that the analyzer 7 is indispensable.
However, the temperature at which the polarizer 5 and the analyzer 7 can be used is normally limited to about 70.degree. C. because they are reduced in performance at higher temperatures. On the other hand, as magnetic sensors are often used in high temperature atmospheres, for example, in substation transformers, they are required to operate at high temperatures of the order of 110.degree. C.